Halftoning is a process by which continuous tone images are approximated by a pattern of pixels that can achieve only a limited number of discrete intensities. An example of this is the rendering of gray tones with black and white pixels, such as in a newspaper photograph. A halftone pattern is made up of a region of pixels referred to as a halftone cell. In conventional digital halftoning (e.g., halftoning that uses rational tangent angles), a halftone cell includes a specific, repeatable pattern. The discrete number of tonal levels of a halftone pattern depends upon the number of pixels in the halftone cell and the number of exposure levels or dot sizes for each pixel.
Halftones yield different optical densities on different paper types, depending on paper characteristics (e.g., coating, pulp, and chemicals used in the manufacturing process). In addition, for a given paper, there exists a fundamental characteristic of an ink printing system, which relates to optical Density (OD) and ink coverage. However, without detailed information about the specifics of the system, such as the drop sizes and halftones for an ink-jet printing system, the characteristic OD versus ink coverage information cannot be determined.
Accordingly, a mechanism to derive an ink model is desired.